Method for producing high shrinking acrylonitrile polymer fibres



TEMPEJATURE Nov. 19, 1963 YOSHIMASA FUJITA ETAL METHOD FOR PRODUCING HIGH SHRINKING ACRYLONITRILE POLYMER FIBRES Filed Aug. 30, 1962 y MWM Attorneys United States Patent 3,111,366 METHUD FQR PRfiDUClNG HlGH SHRINKING ACRYLQNTTRELE PGLYMER FIBRES Yoshimasa Fajita, Nalrano, Saidaiji, and Taltnro Hayshara, Saidaiji, Eapan, assignors to Japan Exlan Company Limited, Kite-kn, @saka, Japm Filed Aug. 30, 1962, Ser- No. 229,461 Claims priority, application Japan Sept. 1, 1961 3 Claims. (Cl. 1848) The present invention relates to the production of polyacrylonitrile fibres with improved properties particularly useful for the so-called high bulk yarns.

Polyacr lonitrile bulky yarns (sometimes referred to also as high-bulk yarns) are generally prepared by blending high-shrinking polyacrylonitri-le staples which have been subjected to a treatment under tension and lowshrinking or substantially non-shrinking staples which have been first treated under tension and then relaxed, and spinning the blended fibres into yarns, which develops bulkiness upon shrinkage of the high-shrinking component or staples when subjected to a heat treatment, for example, in a dyeing operation.

it is conventional that, when a bulky yarn is to be produced from a tow of polyacrylonitrile, the tow is cut into staples under stretching and heating by means, for example, of Pacific Converter and Turbo-Stapler and then the staples are relaxed under heat to prepare low-shrinking fibres. High-shrinking polyacrylonitrile fibres are prepared in the same manner except that no thermal slackening or relaxing is effected after the stretch cutting. High-shrinking fibres may also be produced by omitting a heat-treatment or by effecting the heat-treatment only under mild conditions after the usual stretching stage in the ordinary process of producing polyac-rylonitrile fibres. If desired, natural or synthetic fibres other than those of acrylonitrile may be used as low-shrinking component. The high-shrinking fibres and low-shrinking fibres are blended and spun to obtain a yarn, which, when subjected to heat in the relaxed condition, develops bulkiness.

However, these conventional methods for preparing high-shrinking polyacrylonitrile fibres have various drawbacks. Thus, for example, when Turbo-Stapler or Pacific Converter is employed, the tow must be introduced into a narrow clearance defined by two opposing hot plates so that the tow is stretched under heating during the passage through the clearance. Therefore, the efiect or" the heating and stretching tends to be uneven over the entire tow. Moreover, both the amount of tow that can be processed at a unit time and the rate of passage through the clearance are limited. Furthermore, since the fibres are stretched under dry and hot conditions the knot strength of the fibres is adversely afiected.

When high-shrinking fibres are produced by omitting a heat treatment or by carrying out a mild heat treatment after the usual stretching in the ordinary process of producing polyacryionitrile fibres, voids are created in the fibre structure when the fibres are shrunk under heating after spinning, with the result that the fibres tend to fibrillate. Furthermore, the fibres of this type can not successfully be dyed under mild dyeing conditions.

The principal object of this invention, therefore, is to overcome the above drawbacks and to provide a novel method for the production of high-shrinking polyacrylonitrile fibres having desired properties for use as materials for high-bulk yarns.

Another object of this invention is to provide a novel method for producing high-shrinking polyacrylonitrile fibres with improved properties, said method being characterized by a combination of specific steps under specific 2 conditions in the process for producing polyacrylonitrile fibres.

Other objects, advantages and features of the invention will be apparent from the following detailed description and by refer-ring to the accompanying drawing which is a graph showing the 'dry bulb temperature-rela tive humidity conditions to be used in drying the fibres according to the method of this invention.

Briefly, the method of this invention is characterized by the fact that fibres prepared by extruding an aqueous spinning solution of an acrylonitrile polymer into an aqueous coagulating bath and orientin the formed tow by stretching in a conventional manner are dried under the specific temperature and relative humidity conditions falling within the area defined by the lines AB and C D or" the graph shown in the drawing until substantially all of the water has been removed from the filaments, then the dried filaments are heat treated in an atmosphere of pressurized steam of C. to C. in the relaxed condition, and the resulting fibres are restretched 1.1-1.5 times the length in an atmosphere of pressurized steam of 100 C.-l20 C.

Preferred fibre-forming acrylonitrile polymers to be used in carrying out the method of this invention are those containing a major propontiou (at least 85% by weight) of acrylonitrile. Thus, for example, polymers consisting of acrylonitrile alone or copolymers of acrylonitrile and one or more of vinyl monomers copolymerizable with acryl-onitrile, said copolymers containing predominant proportions (at least 85% by weight) of acrylonit-rile, are preferred. The vinyl monomers copolymerizable with acrylonitrile are well known in the art of acrylonitrile copolyrners and typical examples of the same are methyl acrylate, methyl methaorylate, vinyl acetate, styrene, vinyl chloride, vinyl propionate, styrene sulfonic acid, vinyl pyridines, allyl sulfonate or sulfonic acid, methalilyl sulfonate or sulfonic acid, etc. Therefore, the term po-lyacrylonitrile, acrylonitrile polymer or the like as used in this specification and claims is intended to mean not only polymers of acrylonitrile itself but also copoly-mers of a major proportion (preferably more than 85% by weight) of acrylonitrile and a minor proportion (preferably less than 15% by weight) of vinyl monomer(s) copoly-mer-izable with acrylonitrile,

Solvents to dissolve these acrylonitrile polymers to form spinning solutions should be inorganic or aqueous ones. A concentrated aqueous solution of a water-soluble inorganic salt which yields highly hydrated ions in an aqueous solution is preferred, More specific examples of such water-soluble inorganic salts are Zinc chloride, sodium thiocyanate, calcium thiocyanate, etc. Generally, saturated or nearly saturated (eag. 40-55% by weight) aqueous solutions of such salts may be used. If desired an inorganic acid such as nitric acid, sulfuric acid in the concentration, for example, of 55-75% may be used as the rnediurn for iorming the spinning solutions.

The concentration of the acryloni-trile polymer in the solvent is not critical except that the resulting solution should have a workable viscosity. Generally, the concentration of the polymer in the spinning solution may be from 7 :to 20% by weight.

In forming polyacrylonitrile filaments, the spinning solution is, after filtration and degasification, extruded into a coagulating bath through orifices of a spinnerette in a conventional manner. The coagulating bath should also be of aqueous type and may be water or may consist of a dilute (e.g. less than 35%, preferably 6-15% by weight) aqueous solution of such inorganic salt as mentioned before. The coagulating bath may also comprise a dilute aqueous solution (e.g. 25-35%) of an inorganic acid such as nitric acid or sulfuric acid. Usually, the

3 coagulating bath is maintained at a temperature between 5 C. to C.

The coagulated filaments are then washed with water at room or lower temperature, and stretched to effect the molecular orientation. This stretching operation may be carried out in a well known conventional manner. Thus for example, the filaments are stretched about 6 to 16 times the length in a hot water higher than 80 C. Alternatively it is also possible to carry out the so-called two step stretching operation wherein the filaments are preliminarily stretched 1.5 to 4 times the original length at a temperature from 2 C. to 40 C. preferably at room temperature and are further stretched 3-15 times the length in hot water or steam at a temperature from 70 C. to 100 C.

The preparation of polyacrylonitrile spinning solutions, spinning thereof in an aqueous coagulating bath and the subsequent stretching for orientation are known per se and do not constitute a distinctive feature of the present invention so that any further detailed explanation thereabout will be unnecessary.

The essential and distinctive feature of the present invention is in the subsequent treatment of the oriented filaments as produced above. This operative feature is fully described below.

According to this invention the oriented filaments are then dried. The important feature is in that this drying is carried out in a drying atmosphere under specific conditions of temperature and humidity falling within the area defined by the lines A-B and CD, preferably by the lines A-B and C'D' of the graph shown in the accompanying drawing and that said drying under the said conditions should be continued until substantially all of the water has been evolved from the said filaments. As described in T. H. Robertson et al. US. Patent No. 2,984,912, the structure of the fibre is collapsed or the fibre is made non-structured and densified when the filaments are so dried under the above conditions. This drying operation and the conditions for the same are essential in this invention. If the drying is carried out under the conditions outside the particular range specified above or if not substantially all of the water is removed from the filaments or fibres, the structure tends to be reproduced in the subsequent steam treatment and the desired result is not obtained.

The non-structured dense fibres are then subjected to a heat treatment in high temperature pressurized steam from 105 C. to 160 C. in a relaxed state. The time for this treatment may vary over a wide range, e.g. from 10 seconds to minutes or longer. By this heat treatment there are obtained fibres with improved properties, particularly knot-strength and dyeability, without loss of the advantages of the non-structured dense fibres, namely resistance to fibrillation and uniform dyeability even to the interior central portion of the fibre.

It has been found that in order to obtain high shrinking fibres from the non-structured dense fibres having the improved physical properties and dyeability, without losing these desired properties, it is necessary to re-stretch the fibres in an atmosphere of steam of a temperature from 100 C. to 120 C. Preferably, the fibre is stretched 1.1 to 1.5 times the length in this stage. The conditions under which the re-stretching is effected are critical in method of this invention. Thus, for example, if the restretching is carried out in hot water of a temperature less than 100 C. the resulting fibre, while it may be improved in the tensile strength, loses its knot strength thereby causing troubles in the subsequent spinning operation. Furthermore, the re-stretching in hot water causes the formation of rather extensive voids (being of the order of Lu, visible under a microscope of about X100) in the resulting fibres, said voids being often responsible for the fibrillation and uneven dyeing. In contrast thereto, if the fibres are re-stretched in steam at 100-l20 C. as mentioned above in accordance with this invention, the

4 decrease in knot strength and the undesired formation of voids are avoided with the result that high shrinking fibres retaining the desired properties are readily produced.

The effect of this re-stretching process as combined with the preceding drying and heat treatment in steam would be clear from the following experiments and results:

A copolymer of 90% acrylonitrile and 10% methyl acrylate was dissolved in a 50% aqueous solution of sodium thiocyanate and the resulting spinning solution, after filtration and degasification, was extruded through a spinnerette having 40 holes of 90 microns diameter into a coagulating bath of 10% aqueous solution of sodium thiocyanate maintained at 2 C. The filaments were then washed with water at 5 C. and stretched 10 times the length during the passage through hot water (98 C.). The oriented filaments were then dried in an atmosphere of 105 C., relative humidity 26% until substantially all of the water in the filaments has been removed. Thereafter the filaments were heat treated in stream of 110 C. for 10 minutes. The resulting filaments were then restretched 1.3 times the length under various conditions. The following Table 1 shows the conditions of the restretching operation and the results (relation between the shrinkability and knot strength).

TABLE 1 Re-stretching Shrinkage (percent) in hot Knot Water at strength, Medium Temp, 0. 100 C. in g./d.

relaxed state It should be noted in the Table 1 that even at the same temperature the knot-strength of the resulting fibre remarkably varies depending upon the medium employed. Furthermore, it should be noted that even when steam is used as the heating medium in the stretching process both the knot-strength and shrinkability tend to decrease at too high temperatures. Thus, it is most desirable to carry out the stretching in steam of a temperature from 100 C. to 120 C. The above experiment also indicated that the number of fibres having voids in the structure was smaller or only A in the case where the fibres are restretched in steam as compared with the case where the re-stretch is effected in hot-water.

The above procedures were repeated except that the re-su'etching was carried out in steam of 105 C. with various stretch ratios and there were obtained the results erable that the stretch ratio is from 1.2 to 1.3 times the original length in view of the shrinkability and knot strength.

The filaments or fibres resulting from the above described particular re-stretching process are satisfactory in the knot strength and have no noticeable voids in their structure. They also show excellent dyeability and sutficient shrinkability. These fibres may subsequently be treated in a conventional manner Well known in the m to prepare materials for bulky yarns. Thus, for exmple, the filaments may be mechanically processed to be crimped and the crimped filaments may be cut into desired staple length without the use of Turbo-Stapler or Pacific Converter in a conventional manner. The high shrinking fibrous material thus obtained may be blended with low or non-shrinking material and spun into yarns, which when heat treated in a relaxed state at a temperature higher than the temperature at which the re-stretching was efiected, will become bulky due to the shrinkage of the high shrinking component. The high shrinking polyacrylonitrile fibres are applicable to those uses where known shrinking polyacrylonitrile fibres have been employed.

The following examples illustrate some embodiments of the invention, but the invention is not limited by these examples. All parts are by weight. The Word shrinkability means shrinkage (percent) of the fibre when it is placed in hot water at 100 C. in a relaxed state.

Example 1 A copolymer of 90 parts acrylonitrile and 10 parts methyl acrylate was dissolved in 45% aqueous solution of sodium thiocyanate and the resulting spinning solution, after filtration and degasification, Was extruded through a spinnerette having 8500 holes of 65 microns diameter into a coagulating bath of 12% aqueous solution of sodium thiocyanate maintained at -3 C. The filaments were then washed with water at 5 C. and stretched times the length during the passage though hot water of 90 C. The oriented filaments were then dried in an atmosphere of 105 C., relative humidity 26% until substantially all of the Water in the filaments is removed to obtain non-structured dense filaments. Thereafter the filaments were heat treated in steam of 125 C. in a relaxed state for 5 minutes and then crimped (number of crimps: 12 per inch) by a stuffing box type crimper, and cut into staple length to obtain low shrinking fibres.

The same procedure was repeated except that after spinning, washing, stretching for orientation, drying and heat treating at 125 C. as mentioned above, the tow of a total denier of 500,000 (each filament 3 was passed through a steam cylinder (4 in. length) equipped with a water-seal means to maintain the desired steam pressure, at the rate of 80 m./min. During the passage through the cylinder the tow was stretched 1.3 times the length in steam of 110 C. The stretched filaments were then crimped by a stuffing box type crimper and cut into staple length to obtain high shrinking fibres. The fiber had a fineness of 2.68 denier, dry strength of 2.88 g./d., knot strength of 2.05 g./d. and 11.8 crimps, in average, per inch. The dyeability was substantially comparable with that of the low shrinking fibres.

The high shrinking fibres and low shrinking fibres were blended together in a proportion of 50 to 50, and spun into 18 counts yarn. When the yarn was treated in steam at 115 C. for minutes in a relaxed state it was rendered bulky with shrinkage of 23.4%.

Example 2 A copolymer of 85 parts acrylonitrile, 7.5 parts vinyl acetate and 7.5 parts methyl vinyl pyridine was dissolved in 48% aqueous solution of sodium thiocyanate and the resulting spinning solution, after the usual filtration and degasification, was extruded through a spinnerette having 8500 holes of 70 microns diameter into a coagulating bath of 11.5% aqueous solution of sodium thiocyanate maintained at 2 C. The filaments are then washed with water at 5 C. and stretched 10 times the length during the passage through hot water a C. The oriented filaments were then dried in an atmosphere of 110 C., relative humidity 2728% until substantially all of the Water in the filaments is removed to obtain nonstructured dense filaments. Thereafter the filaments were heat treated in steam of 122 C. in a relaxed state for 5 minutes, and then crimped (number of crimps: 12 per inch) by a stufling box type crimper and cut into staple length to obtain low shrinking fibres.

The same procedure was repeated except that after spinning, washing, stretching for orientation, drying and heat treating at 12 C. as mentioned above, the tow of a total denier of 500,000 (each filament 2 was passed through the steam cylinder of Example 1 at a rate of 60 m./min. while maintaining the steam temperature at C. During the passage through the steam cylinder the tow was stretched 1.2 times the length. The stretched filaments were then crimped by a stufiing box type crimper and cut into staple length to obtain high shrinking fibers. The fibre had a fineness of 1.75 dry strength of 4.35 g./d., knot strength of 2.03 g./d. and 8.5 crimps, in average, per inch. The shrinkability was 22.0%.

The high shrinking fibre and low shrinking fibre were blended together in a proportion of 50 to 50, and spun into 18 counts yarn. When the yarn was treated in steam at C. for 10 minutes in a relaxed state, it was rendered bulky with shrinkage of 25.2%.

Example 3 The procedure of Example 1 was repeated except that a copolymer of 90 parts acrylonitrile, 9.5 parts methyl acrylate and 0.5 part sodium methallyl sulfonate to obtain low shrinking fibres and high shrinking fibres. The high shrinking fibre had a fineness of 2.41 dry strength of 2.82 g./d., knot strength of 2.08 g./d., shrinkability of 24.7% and 12.5 crimps per inch. The high shrinking fibre and low shrinking fibre were blended together in a proportion of 50 to 50 and spun into a yarn of 18 counts. When the yarn Was steam treated at C. for 10 minutes in a relaxed state it was rendered bulky with shrinkage of 25.7%.

What we claim is:

1. Method for producing high shrinking acrylonitrile polymer fibre which comprises (a) drying wet acrylonitrile polymer filaments, prepared by aqueous wet-spinning and subsequent stretching for orientation, in a drying atmosphere under conditions of temperature and humidity defined by the lines AB and CD of the graph shown in the drawing until substantially all Water is removed from said filaments,

(b) heat treating the dried filaments in an atmosphere of pressurized steam at 105 C. to 160 C. in a relaxed state, and

(c) re-stretching the filaments 1.1-1.5 times the length in an atmosphere of pressurized steam at 100 to C.

2. A method as claimed in claim 1, wherein the acrylonitrile polymer contains more than 85% by weight of acrylonitrile.

3. A method as claimed in claim 1, wherein the filaments are stretched 1.2-1.3 times the length in the restretching process.

References Cited in the file of this patent UNITED STATES PATENTS 2,697,023 Martin Dec. 14, 1954 FOREIGN PATENTS 663,500 Great Britain Dec. 19, 1951 

1. METHOD FOR PORUDICNG HIGH SHRINKING ACRYONITRILE POLYMER FIBRE WHICH COMPRISES (A) DRYING WET ACRYLONITRILE POLYMER FILAMENTS, PREPARED BY AQUEOUS WET-SPINNING AND SUBSEQUENT STRETCHING FOR ORIENTATION, INA DRYING ATMOSPHERE UNDER CONDITIONS OF TEMPERATURE AND HUMIDITY DEFINED BY THE LINES A-B AND C-D OF THE GRAPH SHOWN IN THE DRAWING UNTIL SUBSTANTIALLY ALL WATER IS REMOVED FROM SAID FILAMENTS, (B) HEAT TREATING THE DRIED FILAMENTS IN AN ATMOSPHERE OF PRESSURIZED STEAM AT 105*C. TO 160*C. IN A RELAXED STATE, AND (C) RE-STRETCHING THE FILAMENTS 1.1-1.5 TIMES THE LENGTH 